In recent years, there have been proposed and developed various heat-insulated internal combustion engines in which thermal insulation materials such as ceramic materials are affixed to a part or almost the entire wall surface of a combustion chamber. The thermal insulation material contributes to a reduction in cooling loss, thus enhancing a thermal efficiency of the engine at low load operation. One such heat-insulated engine has been disclosed in Japanese document “Proceedings of 13th Internal Combustion Engine Symposium (International), (1996), 68, pp. 399-404, titled “Combustion Chamber and Performance of a Low Heat Rejection Engine” published Jun. 17, 1996 and written by six authors Takatoshi SUGANO, Shigeo SEKIYAMA, Hiroshi SASAKI, Akira HIGASHINO, Hiroshi MATSUOKA, and Hideo KAWAMURA.